1. Field of the Invention
The present invention pertains to photoimaging and, in particular, the use of photoresists (positive-working and/or negative-working) for imaging in the production of semiconductor devices. The present invention also pertains to novel fluorine-containing polymer compositions having high UV transparency (particularly at short wavelengths, e.g., 157 nm) which are useful as base resins in resists and potentially in many other applications.
2. Description of Related Art
Polymer products are used as components of imaging and photosensitive systems and particularly in photoimaging systems such as those described in Introduction to Microlithography, Second Edition by L. F. Thompson, C. G. Willson, and M. J. Bowden, American Chemical Society, Washington, D.C., 1994. In such systems, ultraviolet (UV) light or other electromagnetic radiation impinges on a material containing a photoactive component to induce a physical or chemical change in that material. A useful or latent image is thereby produced which can be processed into a useful image for semiconductor device fabrication.
Although the polymer product itself may be photoactive, generally a photosensitive composition contains one or more photoactive components in addition to the polymer product. Upon exposure to electromagnetic radiation (e.g., UV light), the photoactive component acts to change the rheological state, solubility, surface characteristics, refractive index, color, electromagnetic characteristics or other such physical or chemical characteristics of the photosensitive composition as described in the Thompson et al. publication supra.
For imaging very fine features at the submicron level in semiconductor devices, electromagnetic radiation in the far or extreme ultraviolet (UV) is needed. Positive working resists generally are utilized for semiconductor manufacture. Lithography in the UV at 365 nm (I-line) using novolak polymers and diazonaphthoquinones as dissolution inhibitors is a currently established chip technology having a resolution limit of about 0.35–0.30 micron. Lithography in the far UV at 248 nm using p-hydroxystyrene polymers is known and has a resolution limit of 0.35–0.18 nm. There is strong impetus for future photolithography at even shorter wavelengths, due to a decreasing lower resolution limit with decreasing wavelength (i.e., a resolution limit of 0.18–0.12 micron for 193 nm imaging and a resolution limit of about 0.07 micron for 157 nm imaging). Photolithography using 193 nm exposure wavelength (obtained from an argon fluorine (ArF) excimer laser) is a leading candidate for future microelectronics fabrication using 0.18 and 0.13 μm design rules. Photolithography using 157 nm exposure wavelength (obtained from a fluorine excimer laser) is a leading candidate for future microlithography further out on the time horizon (beyond 193 nm) provided suitable materials can be found having sufficient transparency and other required properties at this very short wavelength. The opacity of traditional near UV and far UV organic photoresists at 193 nm or shorter wavelengths precludes their use in single-layer schemes at these short wavelengths.
Some resist compositions suitable for imaging at 193 nm are known. For example, photoresist compositions comprising cycloolefin-maleic anhydride alternating copolymers have been shown to be useful for imaging of semiconductors at 193 nm (see F. M. Houlihan et al, Macromolecules, 30, pages 6517–6534 (1997); T. Wallow et al., SPIE, Vol. 2724, pages 355–364; and F. M. Houlihan et al., Journal of Photopolymer Science and Technology, 10, No. 3, pages 511–520 (1997)). Several publications are focused on 193 nm resists (i.e., U. Okoroanyanwu et al, SPIE, Vol. 3049, pages 92–103; R. Allen et al., SPIE, Vol. 2724, pages 334–343; and Semiconductor International, September 1997, pages 74–80). Compositions comprising addition polymers and/or ROMP (ring-opening methathesis polymerization) of functionalized norbornenes have been disclosed (e.g., PCT WO 97/33198 (Sep. 12, 1997) to B. F. Goodrich). Homopolymers and maleic anhydride copolymers of norbornadiene and their use in 193 nm lithography have been disclosed (J. Niu and J. Frechet, Angew. Chem. Int. Ed., 37, No. 5, (1998), pages 667–670). Copolymers of flourinated alcohol-substituted polycyclic etylenically unsaturated comonomer and sulfur dioxide that are suitable for 193 nm lithography have been reported (see H. Ito et al., “Synthesis and Evaluation of Alicyclic Backbone Polymers for 193 nm Lithography”, Chapter 16, ACS Symposium Series 706 (Micro- and Nanopatterning Polymers) pages 208–223 (1998), and H. Ito et al., Abstract in Polymeric Materials Science and Engineering Division, American Chemical Society Meeting, Volume 77, Fall Meeting, Sep. 8–11, 1997, held in Las Vegas, Nev.) Because of the presence of repeat units derived from sulfur dioxide in this alternating copolymer, it is not suitable for 157 nm lithography due to the excessively high absorption coefficient of this polymer at 157 nm.
Photoresists containing fluorinated alcohol functional groups attached to aromatic moieties have been disclosed (see K. J. Przybilla et al., “Hexafluoroacetone in Resist Chemistry: A Versatile New Concept for Materials for Deep UV Lithography”, SPIE Vol. 1672, (1992), pages 500–512). While suitable for 248 nm lithography, these resists, because of the aromatic functionality contained in them, are unsuitable for lithography at 193 or 157 nm (due to the excessively high absorption coefficients of the aromatic resist components at these wavelengths).
Resist compositions suitable for imaging at 157 nm are presently unknown. The main reason for this current status of 157 nm resists is that most or all known materials absorb to a significant degree at this wavelength to preclude their use as component(s) in 157 nm resists.
Copolymers of fluoroolefin monomers and cyclic unsaturated monomers are known (U.S. Pat. Nos. 5,177,166 and 5,229,473 to Daikin Industries, Ltd.). These patents do not disclose the use of these copolymers in any photosensitive compositions. Copolymers of certain fluorinated olefins with certain vinyl esters are known. For example, the copolymer of TFE with cyclohexanecarboxylate, vinyl ester is known (Japanese Patent Appl. JP 03281664 to Dainippon Ink and Chemicals). Copolymers of TFE and vinyl esters, such as vinyl acetate, and use of these copolymers in photosensitive compositions for refractive index imaging (e.g., holography) is known (U.S. Pat. No. 4,963,471 to DuPont).
Certain copolymers of fluorinated alcohol comonomers with other comonomers have been reported in U.S. Pat. No. 3,444,148 and JP 62186907 A2 patent publication. These patents are directed to membrane or other non-photosensitve films or fibers, and neither has any teaching of fluorinated alcohol comonomers use in photosensitve layers (e.g., resists).
U.S. Pat. No. 5,655,627 discloses a process for generating a negative tone resist image by coating a silicon wafer with a copolymer resist solution of pentafluoropropyl methacrylate-t-butyl methacrylate in a solvent, and then exposing at 193 nm and developing with a carbon dioxide critical fluid.
There is a critical need though for other novel resist compositions for use at 193 nm, and particularly at 157 nm, or lower that have not only high transparency at these short wavelengths but also suitable other key properties, including good plasma etch resistance and adhesive properties.